Perpetual Pavements

Design and Construction Concepts

Empirical Design

• AASHO road test procedure (1958)

• Updated in 1993 AASHTO Pavement

Guide

• Pavement designed to fail after a certain

number of load repetitions

• Increased number and size of loads require

thicker pavements

Mechanistic Design

Moving toward design tools based

on:

• Strengths of materials

• Stress-strain relationships

Endurance Limit Theory

• Reasearch by Monismith and McLean at

Cal-Berkeley (2) indicates that HMA

exhibits an “endurance Limit” (strain level)

below which fatigue damage does not

accumulate.

Endurance Limit Theory

Thompson and Carpenter, University of Illinois, (1) conclude:

• Data supporting the concept of an endurance limit” for HMA have been presented for a wide variety of mixtures,

• Each mixture may have an individual endurance limit, but in no case has it been shown that a value lower than 70 micro-strain is required

• Data indicating that overloads do not significantly alter the existence of an endurance limit have been presented

Actual pavement performance

• The Transportation Research Laboratory

(UK), Michael Nunn (3) reported that heavy

duty HMA pavements in the UK did not

show fatigue damage , even after carrying

loads far in excess of their original design

• Similar experience in Washington, Ohio

and other US states.

Washington State

Performance Data

• Study of Asphalt Pavements

• I - 90 Spokane to Seattle

• No Reconstruction of Any Pavement for

Structural Reasons

Ohio Performance

• Flexible pavements on Ohio’s Interstate

highways conservatively designed for 20

year life, after nearly 40 years of service,

have never required required replacement or

major rehabilitation.

• In fact the Ohio DOT has never even done a

LCCA for major rehabilitation of a flexible

section.

Conclusion

• It should be possible to design and build

HMA pavements that will never fail in

fatigue and will have indefinite structural

life

• The Perpetual Pavement Concept

Pavement Design Concepts

• Fatigue Resistant Asphalt Base

– Minimize Tensile Strain with Pavement

Thickness and/or higher strength

– Thicker/stronger Pavement = Lower Strain

– Strain Below Fatigue Limit = Indefinite Life

Compressive

Strain

Tensile

Strain

Strain

Fatigue Life

Indefinite

Fatigue

Life

• Fatigue Resistant Asphalt Base

– High Asphalt Content Mixes = Greater Strain

Capability

– Modified Binders = Greater Strain Capability

Pavement Design Concepts

Fatigue Life

Strain

High Asphalt

Content

Low Asphalt

Content

Indefinite

Fatigue

Life

Pavement Design Concepts

• Bottom-up Design and Construction

• Foundation

– Stable Paving Platform – prepared, drained

– Minimize Seasonal Variability and Volume

Change in Service

• Fatigue Resistant Lower Asphalt Layer

• Rut Resistant Upper Asphalt Layers

Pavement Design Concepts

Max Tensile

Strain

Pavement

Foundation

High Modulus

Rut Resistant Material

4.5 - 6”

Flexible Fatigue Resistant

Material 3 - 4”

1.5 - 3” SMA, OGFC or Superpave

} 4”

to

6”

Zone

of

High

Compression

Perpetual Pavement

Design Concepts

Existing

Designed to fail after

load repetitions

Designed to withstand

ultimate load

Mechanistic design

principles employed

3-layer design system

Empirical design

principles employed

2 - layer design

Absolutely Asphalt …For Cost, For Convenience, For Comfort !!

Perpetual Pavement

• Structure Lasts 50+ years.

– Bottom-Up Design and Construction

– Indefinite Fatigue Life

• Renewable Pavement Surface.

– High Rutting Resistance

– Tailored for Specific Application

• Consistent, Smooth and Safe Driving

Surface.

• Avoids Costly Reconstruction.

Perpetual Pavement

Summary

By designing for the fatigue limit of the

material rather than traffic repetitions.

By employing mechanistic design principles.

By using a 3-layer design

build a Perpetual Pavement

Absolutely Asphalt …For Cost, For Convenience, For Comfort !!

The Ohio Demonstration Project

• Relocated US 30 at Wooster

• Open to traffic December , 2005

• 16 ½ inch thick HMA, 3-layer design

• Fully instrumented, for environmental factors, loads, deflection

• Materials and design assumptions to be evaluated through research.

The Ohio Demonstration Project

US 30 Perpetual Pavement

Demonstration Project

The Ohio Demonstration Project

Instrumentation:

• Weigh-in-motion scales

• Deflection measurement

• Load cells

• Strain gages at every level of the pavement

• Temperature and moisture measurement

throughout

The Ohio Demonstration Project

PerRoad Express

• PerRoadXpress is an easy-to-use, all-on-

one-screen program for designing Perpetual

Pavements for low- and medium-volume

roads and parking lots.

• http://www.eng.auburn.edu/users/timmdav/

PerRoadXPress.msi

For more Information

• www.flexiblepavements.org

• Ohio Asphalt magazine

References

1. Fatigue Design Principles for Long Lasting

HMA Pavements, Thompson and Carpenter

2. Technology of Thick Lift Construction:

Structural Design Considerations, Monismith and

McLean, Proceedings, AAPT, Vol. 41, 1972

3. Long Life Flexible Pavements, proceedings

Eighth International Conference on Asphalt

Pavements, 1997

Questions?

• About Perpetual Pavement?

• Anything else?